I had to post an article on this because I just got done done reading an article on visihow that was complete crap and provided no help to anyone. It basically stated that it's probably because you're eating a soy based diet and now you're estrogen is too high... I can't wait to knife fight the writer of that horrible article (we bloggers do that from time to time). You want to know how to grow a beard if you can't, the answer is increase Testosterone & take Minoxidil.
Now I'm not saying you should go to your local drug dealer and see if they've got a fresh batch of steroids in, what I'm saying is that most men suffer from low T and don't know it. One of the biggest notable effects of that is very little body hair growth (facial hair falls into this category). If you don't have the money to go to the doctor, get your blood work done and actually see where your levels are then do the responsible thing and get a natural testosterone booster. These things are filled with extracts that have been proven to increase testosterone thus increasing your body hair to beast mode.
As for the minoxidil, that's just the clinical name for Rogaine. Guys have been using it for years on there head and then somewhere along the way one of them got a bright idea to use it on their face and what the hell do you know it worked! This is something I firmly believe in because it's worked not only on my face but my head too. Nothing worse that having a thinning head of hair and a thick beard in my opinion.